Oxyalkylene polymers having reactive silicon groups are curable by the moisture in the air at room temperature yielding a rubbery substance similar to a room temperature curable silicone rubber. The cured substance is useful as a sealant, adhesive and the like owing to its excellent elongation, tensile strength, and adhesion.
One of the characteristics of polymers having reactive silicon groups is the advantage that, because the main chain is composed of an oxyalkylene polymer, almost all kinds of paints can be applied to the cured substance thereof. Incidentally, coating of silicone rubbers with paints is virtually impossible due to the water- and oil repellent nature of silicone rubber.
Cured products of a composition of an oxyalkylene polymer having reactive silicon groups, however, sometimes cause insufficient drying (hardening) of coated alkyd paints, and therefore it is virtually impossible to coat the cured products with the paints. As a result, in such a case attempts to coat a cured sealant of oxyalkylene polymer that contains plasticizers with alkyd paints were almost given up.
Alkyd paints, however, are used in various applications because of advantages in almost all respects over oil paints, e.g., by quick drying, hard and glossy films, excellent properties including adhesion, weathering resistance, oil resistance, and widely adjustable properties, through selection of the kinds of modifying drying oils, oil length and modes of modification. Therefore it is very advantageous for cured products of oxyalkylene polymers to be coated with alkyd paints.
At the beginning, even the cause of the poor drying property was entirely unclear. However, the present inventors, after a diligent study of the cause, found that incorporation of low molecular weight plasticizers in a curable composition comprising an oxyalkylene polymer having reactive silicon groups impairs the drying property. Plasticizers are used where it is neccessary to lower the viscosity of the composition (to improve workability at the time of application) or to improve the tensile property of the cured substance. Since it is simple to use plasticizers for lowering viscosity or improving the tensile property, the present inventors, after searching for materials which do not impair the drying property of alkyd paints, found that the above problem is eased by the use of a high molecular weight plasticizer.
Among high molecular weight plasticizers, oxyalkylene polymers are superior plasticizers since they are cheap and the cured products have excellent tensile properties at low temperature.
The present inventors have examined various oxyalkylene polymers, and found that when a specific oxyalkylene polymer is used as a plasticizer for an oxyalkylene polymer having reactive silicon groups, the cured product has a highly improved drying property.